With the new interface for iOS (iPhone, iPad), adds Facebook function automatically detects video (AutoPlay) on the News Feed. But if you use the 3G network is not very good, you should remove this feature as it would be difficult to implement. Please follow these steps

Step 1: At the main menu of iPhone, iPad, Click Settings. (Below image)

Step 2: Next Click Facebook then choose Settings. (Below image)

Step 3: Next click Auto-play Video on WiFi only. (Below image)

Now anytime you log in your Facebook on iOS via 3G, this Autoplay Video function will not automatically play. So interesting it is!